Re: [PATCH v2 4/6] mmc: pwrseq_simple: Add optional reference clock support

[Ulf Hansson <ulf.hansson@linaro.org>]

On 28 January 2015 at 19:15, Javier Martinez Canillas
<javier.martinez@collabora.co.uk> wrote:
> Some WLAN chips attached to a SDIO interface, need a reference clock.
>
> Since this is very common, extend the prseq_simple driver to support
> an optional clock that is enabled prior the card power up procedure.
>
> Note: the external clock is optional. Thus an error is not returned
> if the clock is not found.
>
> Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
> ---
>
> Changes since v1:
>  - Rebase on top of latest changes.
>  - Use IS_ERR() instead of checking for NULL to see if the clock exists.
> ---
>  drivers/mmc/core/pwrseq_simple.c | 34 ++++++++++++++++++++++++++++++++--
>  1 file changed, 32 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/core/pwrseq_simple.c b/drivers/mmc/core/pwrseq_simple.c
> index e53d3c7e059c..5e34c77efa5e 100644
> --- a/drivers/mmc/core/pwrseq_simple.c
> +++ b/drivers/mmc/core/pwrseq_simple.c
> @@ -7,6 +7,7 @@
>   *
>   *  Simple MMC power sequence management
>   */
> +#include <linux/clk.h>
>  #include <linux/kernel.h>
>  #include <linux/slab.h>
>  #include <linux/device.h>
> @@ -20,6 +21,7 @@
>
>  struct mmc_pwrseq_simple {
>         struct mmc_pwrseq pwrseq;
> +       struct clk *ext_clk;

You need to add a bool, maybe call it clk_enabled;  See why below.

>         int nr_gpios;
>         struct gpio_desc *reset_gpios[0];
>  };
> @@ -39,6 +41,9 @@ static void mmc_pwrseq_simple_pre_power_on(struct mmc_host *host)
>         struct mmc_pwrseq_simple *pwrseq = container_of(host->pwrseq,
>                                         struct mmc_pwrseq_simple, pwrseq);
>
> +       if (!IS_ERR(pwrseq->ext_clk))
> +               clk_prepare_enable(pwrseq->ext_clk);
> +

There are no guarantee that the ->mmc_pwrseq_simple_pre_power_on()
will be invoked prior ->mmc_pwrseq_simple_power_off().

That means you need to keep track of if you have gated/ungated the
clock. In other words check pwrseq->clk_enabled. That will prevent
potential clk unbalance issues.

>         mmc_pwrseq_simple_set_gpios_value(pwrseq, 1);
>  }
>
> @@ -50,6 +55,17 @@ static void mmc_pwrseq_simple_post_power_on(struct mmc_host *host)
>         mmc_pwrseq_simple_set_gpios_value(pwrseq, 0);
>  }
>
> +static void mmc_pwrseq_simple_power_off(struct mmc_host *host)
> +{
> +       struct mmc_pwrseq_simple *pwrseq = container_of(host->pwrseq,
> +                                       struct mmc_pwrseq_simple, pwrseq);
> +
> +       mmc_pwrseq_simple_set_gpios_value(pwrseq, 1);
> +
> +       if (!IS_ERR(pwrseq->ext_clk))
> +               clk_disable_unprepare(pwrseq->ext_clk);

Same comment as above.

> +}
> +
>  static void mmc_pwrseq_simple_free(struct mmc_host *host)
>  {
>         struct mmc_pwrseq_simple *pwrseq = container_of(host->pwrseq,
> @@ -60,6 +76,9 @@ static void mmc_pwrseq_simple_free(struct mmc_host *host)
>                 if (!IS_ERR(pwrseq->reset_gpios[i]))
>                         gpiod_put(pwrseq->reset_gpios[i]);
>
> +       if (!IS_ERR(pwrseq->ext_clk))
> +               clk_put(pwrseq->ext_clk);
> +
>         kfree(pwrseq);
>         host->pwrseq = NULL;
>  }
> @@ -67,7 +86,7 @@ static void mmc_pwrseq_simple_free(struct mmc_host *host)
>  static struct mmc_pwrseq_ops mmc_pwrseq_simple_ops = {
>         .pre_power_on = mmc_pwrseq_simple_pre_power_on,
>         .post_power_on = mmc_pwrseq_simple_post_power_on,
> -       .power_off = mmc_pwrseq_simple_pre_power_on,
> +       .power_off = mmc_pwrseq_simple_power_off,
>         .free = mmc_pwrseq_simple_free,
>  };
>
> @@ -85,6 +104,14 @@ int mmc_pwrseq_simple_alloc(struct mmc_host *host, struct device *dev)
>         if (!pwrseq)
>                 return -ENOMEM;
>
> +       pwrseq->ext_clk = clk_get(dev, "ext_clock");
> +       if (IS_ERR(pwrseq->ext_clk) &&
> +           PTR_ERR(pwrseq->ext_clk) != -ENOENT &&
> +           PTR_ERR(pwrseq->ext_clk) != -ENOSYS) {

I don't think you can get -ENOSYS.

> +               ret = PTR_ERR(pwrseq->ext_clk);
> +               goto free;
> +       }
> +
>         for (i = 0; i < nr_gpios; i++) {
>                 pwrseq->reset_gpios[i] = gpiod_get_index(dev, "reset", i,
>                                                          GPIOD_OUT_HIGH);
> @@ -96,7 +123,7 @@ int mmc_pwrseq_simple_alloc(struct mmc_host *host, struct device *dev)
>                         while (--i)
>                                 gpiod_put(pwrseq->reset_gpios[i]);
>
> -                       goto free;
> +                       goto clk_put;
>                 }
>         }
>
> @@ -105,6 +132,9 @@ int mmc_pwrseq_simple_alloc(struct mmc_host *host, struct device *dev)
>         host->pwrseq = &pwrseq->pwrseq;
>
>         return 0;
> +clk_put:
> +       if (!IS_ERR(pwrseq->ext_clk))
> +               clk_put(pwrseq->ext_clk);
>  free:
>         kfree(pwrseq);
>         return ret;
> --
> 2.1.3
>

Kind regards
Uffe